MHD power generators have been investigated in the Electrotechnical Laboratory as one of National Research and Development programs. A turbo-expander has been developed for a part of the helium refrigerator to cool the super-conducting magnet for the MHD power generator. The turbo-expander uses externally pressurized gas bearings of low temperature helium to operate the system at a low temperature. An alternator of 4.0kW is employed for the brake of the turbo-expander. The outside diameter of turbine is 40mm and the diameter of rotor with magnets is 30mm. The turbo-expander can be rotated smoothly up to the speed of 120, 000rpm at low temperature when the gas pressure of bearing is 11ata and the flow rate is less than 28m3/hr. The output power of the turbine is 1.3kW when the outlet temperature and pressure are 9.5°K and 0.53ata, respectively. A big liquener of 2001/hr has been designed utilizing the turbo-expanders. The liquefier will be used for the MHD power generator of 1, 000kW.
